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% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
% http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-module(couch_work_queue).
-behaviour(gen_server).
-include("couch_db.hrl").
% public API
-export([new/1, queue/2, dequeue/1, dequeue/2, close/1, item_count/1, size/1]).
% gen_server callbacks
-export([init/1, terminate/2]).
-export([handle_call/3, handle_cast/2, code_change/3, handle_info/2]).
-record(q, {
queue = queue:new(),
blocked = [],
max_size,
max_items,
items = 0,
size = 0,
work_waiters = [],
close_on_dequeue = false,
multi_workers = false
}).
new(Options) ->
gen_server:start_link(couch_work_queue, Options, []).
queue(Wq, Item) when is_binary(Item) ->
gen_server:call(Wq, {queue, Item, byte_size(Item)}, infinity);
queue(Wq, Item) ->
gen_server:call(Wq, {queue, Item, ?term_size(Item)}, infinity).
dequeue(Wq) ->
dequeue(Wq, all).
dequeue(Wq, MaxItems) ->
try
gen_server:call(Wq, {dequeue, MaxItems}, infinity)
catch
_:_ -> closed
end.
item_count(Wq) ->
try
gen_server:call(Wq, item_count, infinity)
catch
_:_ -> closed
end.
size(Wq) ->
try
gen_server:call(Wq, size, infinity)
catch
_:_ -> closed
end.
close(Wq) ->
gen_server:cast(Wq, close).
init(Options) ->
Q = #q{
max_size = couch_util:get_value(max_size, Options, nil),
max_items = couch_util:get_value(max_items, Options, nil),
multi_workers = couch_util:get_value(multi_workers, Options, false)
},
{ok, Q}.
terminate(_Reason, #q{work_waiters=Workers}) ->
lists:foreach(fun({W, _}) -> gen_server:reply(W, closed) end, Workers).
handle_call({queue, Item, Size}, From, #q{work_waiters = []} = Q0) ->
Q = Q0#q{size = Q0#q.size + Size, % increment_queue_size(Q0, Item),
items = Q0#q.items + 1,
queue = queue:in({Item, Size}, Q0#q.queue)},
case (Q#q.size >= Q#q.max_size) orelse
(Q#q.items >= Q#q.max_items) of
true ->
{noreply, Q#q{blocked = [From | Q#q.blocked]}};
false ->
{reply, ok, Q}
end;
handle_call({queue, Item, Size}, _From, #q{work_waiters = [{W, _Max} | Rest]} = Q) ->
gen_server:reply(W, {ok, [Item], Size}),
{reply, ok, Q#q{work_waiters = Rest}};
handle_call({dequeue, Max}, From, Q) ->
#q{work_waiters = Workers, multi_workers = Multi, items = Count} = Q,
case {Workers, Multi} of
{[_ | _], false} ->
exit("Only one caller allowed to wait for this work at a time");
{[_ | _], true} ->
{noreply, Q#q{work_waiters=Workers ++ [{From, Max}]}};
_ ->
case Count of
0 ->
{noreply, Q#q{work_waiters=Workers ++ [{From, Max}]}};
C when C > 0 ->
deliver_queue_items(Max, Q)
end
end;
handle_call(item_count, _From, Q) ->
{reply, Q#q.items, Q};
handle_call(size, _From, Q) ->
{reply, Q#q.size, Q}.
deliver_queue_items(Max, Q) ->
#q{
queue = Queue,
items = Count,
size = Size,
close_on_dequeue = Close,
blocked = Blocked
} = Q,
case (Max =:= all) orelse (Max >= Count) of
false ->
{Items, Size2, Queue2, Blocked2} = dequeue_items(
Max, Size, Queue, Blocked, []),
Q2 = Q#q{
items = Count - Max, size = Size2, blocked = Blocked2, queue = Queue2
},
{reply, {ok, Items, Size - Size2}, Q2};
true ->
lists:foreach(fun(F) -> gen_server:reply(F, ok) end, Blocked),
Q2 = Q#q{items = 0, size = 0, blocked = [], queue = queue:new()},
Items = [Item || {Item, _} <- queue:to_list(Queue)],
case Close of
false ->
{reply, {ok, Items, Size}, Q2};
true ->
{stop, normal, {ok, Items, Size}, Q2}
end
end.
dequeue_items(0, Size, Queue, Blocked, DequeuedAcc) ->
{lists:reverse(DequeuedAcc), Size, Queue, Blocked};
dequeue_items(NumItems, Size, Queue, Blocked, DequeuedAcc) ->
{{value, {Item, ItemSize}}, Queue2} = queue:out(Queue),
case Blocked of
[] ->
Blocked2 = Blocked;
[From | Blocked2] ->
gen_server:reply(From, ok)
end,
dequeue_items(
NumItems - 1, Size - ItemSize, Queue2, Blocked2, [Item | DequeuedAcc]).
handle_cast(close, #q{items = 0} = Q) ->
{stop, normal, Q};
handle_cast(close, Q) ->
{noreply, Q#q{close_on_dequeue = true}}.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_info(X, Q) ->
{stop, X, Q}.
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